In numerous cases, the parenteral administration of active pharmaceutical principles may be preferred to oral absorption, particularly when the medicine to be administered partially or totally decomposes in the digestive system or when a rapid response of the organism is sought.
Parenteral administration of medical principles has, however, certain drawbacks. One of these drawbacks lies in the discomfort experienced by the patient to whom the active principle is being administered. Indeed, parenteral preparations generally take the form of a large volume of liquid in which the medicine is in suspension or dissolved. When the medicine is not very soluble or difficult to pass into suspension, or even when the active principle has to be administered in large doses, a relatively large volume of liquid has to be injected. The ratio between the active principle and the excipient is usually comprised between one percent and one per thousand. The discomfort experienced by the patient thus results both from the size of the needle and the volume of liquid to be injected. In some cases, the very nature of the excipient can also cause the patient suffering.
Another drawback of administering medicine dissolved or in suspension in a liquid medium lies in the fact that the medicine is often unstable in the liquid. The medicine and the liquid must thus be mixed shortly prior to the injection. This can prove particularly disadvantageous when, for example, hundreds of people have to be treated in a small period of time to wipe out an epidemic (administration of a vaccine).
In order to overcome the aforementioned drawbacks, medicines in solid rather than liquid form have been used in order to develop slow release or controlled release preparations. The preparation takes the form of an implant or a rod that is directly injected using a trocar. This type of implant has to enclose the daily dose of medicine multiplied by the number of days of activity, and the quantity of medium sufficient to control the speed of release of the medicine for the time period concerned. Consequently, these solid preparations for injection require a much larger needle than the needles ordinarily used with syringes, which leads to painful injections.
The security injection device disclosed in European Patent No. 0 783 342 overcomes this last drawback. It will be briefly described in conjunction with FIG. 1 annexed to the present Patent Application, which is a cross-section of this type of injection device in the rest position thereof.
Designated as a whole by the general reference numeral 1, the injection device shown in FIG. 1 includes a body 2, which is fixed to a needle 4 via coupling means 6. A rod 8 is driven in translation inside needle 4 and is stopped against a dose 10 of medicinal substance arranged inside said needle 4. A hollow sheath 12 surrounds needle 4 such that the latter is not exposed prior to use. Rod 8 includes a raised portion 14, which limits the travel thereof in body 2. The body 2 includes a collar 16 for facilitating withdrawal of device 1 after injection. A piston 18 is secured to the proximal end of rod 8 and is arranged to slide in a proximal end of body 2. It includes a collar 20. Hollow sheath 12 is placed so as to slide at the distal end of body 2 to enclose needle 4 when it is in the exit position.
The operation of injection device 1 briefly described above is as follows. When the device is pressed against the patient's skin, sheath 12 slides over body 2, thereby exposing needle 4 and allowing the latter to penetrate the skin, while piston 18 and rod 8, arranged as to be able to slide, hold the medicine under the skin when needle 4 is removed.
The solid medicine to be injected is for immediate assimilation by the body. Thus, since the injected quantities are only those necessary to obtain an immediate effect, the needle can be as fine as those of conventional syringes. The injection is less painful insofar as the volume injected is considerably less than the volume necessary for an injection in liquid form. Moreover, the needle of the injection device is not exposed to external elements. Consequently, the needle cannot collect contaminating agents present in the atmosphere or prick anyone inadvertently. Likewise, it is not possible to inadvertently inject a fraction of the medicine or the patient's blood into a member of hospital personnel.
A seal 22 can seal aperture 24 via which needle 4 emerges from injection device 1 in order to preserve the sterility of said needle 4 and the medicinal dose 10. This seal 22 can be made of a brittle material such as biocompatible and biodegradable wax. Alternatively, aperture 24 can be sealed using a cap completely covering sleeve 12.
These means for sealing injection device 1 are not satisfactory. In the case of a wax cap, since there is a non-negligible risk of some of the material remaining caught on the needle and injected into the patient's skin, the manufacturer has to demonstrate the absence of any interaction between the wax and the injected medicine. In the case of a cap, there is a risk of the implant falling at the moment when the said cap is removed.
There therefore existed a need, in the state of the art, for means of preventing the implant falling prior to use of the injection device, particularly during periods of storage and during handling of said injection device prior to carrying out the actual injection.
It is an object of the present invention to answer this need in addition to others by providing an injection device for injecting a solid medicine, including a body inside which there moves a bevelled needle, into which the medicine is introduced, this injection device further including retaining means for preventing the medicine falling prior to injection, characterized in that the medicine is retained via an elastic deformation of the needle imparted by the retaining means or via an elastic deformation of the retaining means themselves, or via a combination of the flexibility of these two means.